: The number of cardiac surgical procedures performed annually on neonates and infants in recent years has steadily increased. Corresponding to the increasing number of procedures has been the increase in the need to provide temporary circulatory support for some of these patients. A current common practice is to support these patients with extracorporeal membrane oxygenation circuitry (ECMO), even when the indications for support are purely cardiac, due to the clinical unavailability of circulatory support devices appropriate for the neonatal and infant patient populations other than the intraaortic balloon pump (IABP). Various ECMO programs report that between one-fourth to one-third of their use of ECMO is for cases where solely cardiac support was required. Only a 42% survival rate has been achieved in this group of patients, the lowest for all categories of ECMO use. To improve the outcome of pediatric patients requiring circulatory support, efforts are being made to develop reliable continuous flow (CF) and pulsatile flow (PF) ventricular assist devices (VADs) appropriate for neonates and infants. New data also suggest that the IABP may be more effective in providing pulsatile left ventricular assistance (LVA) in pediatric patients than previously believed. Consequently, the anticipated availability of an infant VAD for cases where only cardiac support is required is a very attractive alternative to the current cumbersome, labor-intensive, and expensive ECMO circuitry that is often associated with a high complication rate. However, if these VADs are to be clinically acceptable, they must be as, or more, efficacious than ECMO. Our hypothesis is that pulsatile flow LVA in neonates and infants is therapeutically superior to ECMO. To date there has been no systematic evaluation of the physiologic efficacy of ECMO compared to alternative methods for infant LVA using clinically relevant physiologic parameters. Experiments using an acutely prepared, infant animal model of left ventricular dysfunction will compare the efficacy of ECMO to CF and PF assist devices and the IABP by determining the ability of each assistance technique to: 1) restore an acceptable hemodynamic state, 2) restore end-organ perfusion, 3) reduce myocardial oxygen consumption, and 4) maintain adequate mixed venous oxygen saturation. The anticipated result of this research will be clinically relevant physiologic data (blood pressures and flows, tissue perfusion, myocardial oxygen consumption, cardiac chamber volumes, oxygen saturation and delivery) that will indicate that these new devices for infant LVA are superior to ECMO, with pulsatile flow delivery being the most therapeutically effective approach. This new information will result in the consideration of alternatives to ECMO to improve the outcome of pediatric patients requiring LVA.